Add no-irregular-whitespace

docs/user-guide/rules/list.md

@@ -395,3 +395,4 @@ Grouped first by the following categories and then by the [_thing_](http://apps.
 - [`no-missing-end-of-source-newline`](../../../lib/rules/no-missing-end-of-source-newline/README.md): Disallow missing end-of-source newlines (Autofixable).
 - [`no-empty-first-line`](../../../lib/rules/no-empty-first-line/README.md): Disallow empty first lines (Autofixable).
 - [`unicode-bom`](../../../lib/rules/unicode-bom/README.md): Require or disallow Unicode BOM.
+- [`no-irregular-whitespace`](../../../lib/rules/no-irregular-whitespace/README.md): Disallow irregular whitespace.

lib/rules/index.js

@@ -245,6 +245,7 @@ const rules = {
 	'no-invalid-position-at-import-rule': importLazy(() =>
 		require('./no-invalid-position-at-import-rule'),
 	)(),
+	'no-irregular-whitespace': importLazy(() => require('./no-irregular-whitespace'))(),
 	'no-missing-end-of-source-newline': importLazy(() =>
 		require('./no-missing-end-of-source-newline'),
 	)(),

lib/rules/no-irregular-whitespace/README.md

@@ -0,0 +1,114 @@
+# no-irregular-whitespace
+
+Disallow irregular whitespace
+
+<!-- prettier-ignore -->
+```css
+    .firstClass .secondClass {}
+/************* ↑
+ * Irregular whitespace. Selector would fail to match '.firstClass' */
+```
+
+## Options
+
+### `true`
+
+The following patterns are considered violations:
+
+<!-- prettier-ignore -->
+```css
+  .firstClass .secondClass {}
+```
+
+The following patterns are _not_ considered violations:
+
+<!-- prettier-ignore -->
+```css
+  .firstClass .secondClass { /* Writing comments with irregular whitespaces */ }
+```
+
+## Optional secondary options
+
+### `allow: ["\u0085"]`
+
+The members of the array will be ignored by the rule
+
+For example with `"/u180E"`
+
+Given:
+
+```
+["/u180E"]
+```
+
+The following pattern are considered violation:
+
+<!-- prettier-ignore -->
+```css
+a[title="irregular' + '\u00A0' + 'whitespace"] { color: pink; }
+```
+
+The following pattern is _not_ considered violation:
+
+<!-- prettier-ignore -->
+```css
+a[title="irregular' + '\u180E' + 'whitespace"] { color: pink; }
+```
+
+### `only: ["\00A0"]`
+
+Only the members of the array will detected by the rule (see `Unicode reference of irregular whitespaces`)
+
+For example with `"/00A0"`
+
+Given:
+
+```
+["/00A0"]
+```
+
+The following pattern are considered violation:
+
+<!-- prettier-ignore -->
+```css
+a[title="irregular' + '\u00A0' + 'whitespace"] { color: pink; }
+```
+
+The following patterns is _not_ considered violation:
+
+<!-- prettier-ignore -->
+```css
+a[title="irregular' + '\u180E' + 'whitespace"] { color: pink; }
+```
+
+<!-- prettier-ignore -->
+```css
+a[title="irregular' + '\u2002' + 'whitespace"] { color: pink; }
+```
+
+## Unicode reference of irregular whitespaces
+
+\u000B - Line Tabulation (\v) - <VT>
+\u000C - Form Feed (\f) - <FF>
+\u00A0 - No-Break Space - <NBSP>
+\u0085 - Next Line
+\u1680 - Ogham Space Mark
+\u180E - Mongolian Vowel Separator - <MVS>
+\ufeff - Zero Width No-Break Space - <BOM>
+\u2000 - En Quad
+\u2001 - Em Quad
+\u2002 - En Space - <ENSP>
+\u2003 - Em Space - <EMSP>
+\u2004 - Tree-Per-Em
+\u2005 - Four-Per-Em
+\u2006 - Six-Per-Em
+\u2007 - Figure Space
+\u2008 - Punctuation Space - <PUNCSP>
+\u2009 - Thin Space
+\u200A - Hair Space
+\u200B - Zero Width Space - <ZWSP>
+\u2028 - Line Separator
+\u2029 - Paragraph Separator
+\u202F - Narrow No-Break Space
+\u205f - Medium Mathematical Space
+\u3000 - Ideographic Space